Fix map drag around the poles (projection singularity)

Author: EosBandi

.gitignore

@@ -46,3 +46,5 @@ docs/
 obj2/
 obj3/
 
+/.claude/settings.local.json
+/CLAUDE.md

GCSViews/FlightData.cs

@@ -55,6 +55,7 @@ public partial class FlightData : MyUserControl, IActivate, IDeactivate
         internal GMapMarker CurrentGMapMarker;
 
         internal PointLatLng MouseDownStart;
+        internal Point MouseDownStartLocal;
 
         //The file path of the selected script
         internal string selectedscript = "";
@@ -2933,6 +2934,7 @@ private void gMapControl1_Click(object sender, EventArgs e)
         private void gMapControl1_MouseDown(object sender, MouseEventArgs e)
         {
             MouseDownStart = gMapControl1.FromLocalToLatLng(e.X, e.Y);
+            MouseDownStartLocal = e.Location;
             Console.WriteLine("gMapControl1_MouseDown "+ MouseDownStart);
 
             if (ModifierKeys == Keys.Control)
@@ -2971,13 +2973,26 @@ private void gMapControl1_MouseMove(object sender, MouseEventArgs e)
         {
             if (e.Button == MouseButtons.Left)
             {
-                PointLatLng point = gMapControl1.FromLocalToLatLng(e.X, e.Y);
+                // incremental delta avoids direction lock near pole/singularity regions
+                int dx = e.X - MouseDownStartLocal.X;
+                int dy = e.Y - MouseDownStartLocal.Y;
 
-                double latdif = MouseDownStart.Lat - point.Lat;
-                double lngdif = MouseDownStart.Lng - point.Lng;
+                if (dx == 0 && dy == 0)
+                    return;
+
+                double absLat = Math.Abs(gMapControl1.Position.Lat);
+                PointLatLng newCenter = gMapControl1.FromLocalToLatLng(
+                    gMapControl1.Width / 2 - dx,
+                    gMapControl1.Height / 2 - dy);
+
+                if (!double.IsNaN(newCenter.Lat) && !double.IsNaN(newCenter.Lng) &&
+                    !double.IsInfinity(newCenter.Lat) && !double.IsInfinity(newCenter.Lng))
+                {
+                    gMapControl1.Position = newCenter;
+                }
 
-                gMapControl1.Position = new PointLatLng(center.Position.Lat + latdif,
-                    center.Position.Lng + lngdif);
+                // consume this step (critical for stable drag)
+                MouseDownStartLocal = e.Location;
             }
             else
             {

GCSViews/FlightPlanner.cs

@@ -125,6 +125,7 @@ private void but_mincommands_Click(object sender, System.EventArgs e)
         private DateTime mapupdate = DateTime.MinValue;
         private string mobileGpsLog = string.Empty;
         private PointLatLng MouseDownStart;
+        private Point MouseDownStartLocal;
         private PointLatLngAlt mouseposdisplay = new PointLatLngAlt(0, 0);
         private WPOverlay wpOverlay;
         private bool polygongridmode;
@@ -1035,7 +1036,9 @@ public void redrawPolygonSurvey(List<PointLatLngAlt> list)
                     if (now == null || next == null)
                         continue;
 
-                    var mid = new PointLatLngAlt((now.Lat + next.Lat) / 2, (now.Lng + next.Lng) / 2, 0);
+                    var p1 = MainMap.FromLatLngToLocal(now);
+                    var p2 = MainMap.FromLatLngToLocal(next);
+                    var mid = new PointLatLngAlt(MainMap.FromLocalToLatLng((int)((p1.X + p2.X) / 2), (int)((p1.Y + p2.Y) / 2)));
 
                     var pnt = new GMapMarkerPlus(mid);
                     pnt.Tag = new midline() {now = now, next = next};
@@ -1480,8 +1483,10 @@ public void writeKML()
                             if (now == null || next == null)
                                 continue;
 
-                            var mid = new PointLatLngAlt((now.Lat + next.Lat) / 2, (now.Lng + next.Lng) / 2,
-                                (now.Alt + next.Alt) / 2);
+                            var p1 = MainMap.FromLatLngToLocal(now);
+                            var p2 = MainMap.FromLatLngToLocal(next);
+                            var mid = new PointLatLngAlt(MainMap.FromLocalToLatLng((int)((p1.X + p2.X) / 2), (int)((p1.Y + p2.Y) / 2)));
+                            mid.Alt = (now.Alt + next.Alt) / 2;
 
                             var pnt = new GMapMarkerPlus(mid);
                             pnt.Tag = new midline() {now = now, next = next};
@@ -1557,7 +1562,9 @@ public void writeKML()
                                 if (now == null || next == null)
                                     continue;
 
-                                var mid = new PointLatLngAlt((now.Lat + next.Lat) / 2, (now.Lng + next.Lng) / 2, 0);
+                                var p1 = MainMap.FromLatLngToLocal(now);
+                                var p2 = MainMap.FromLatLngToLocal(next);
+                                var mid = new PointLatLngAlt(MainMap.FromLocalToLatLng((int)((p1.X + p2.X) / 2), (int)((p1.Y + p2.Y) / 2)));
 
                                 var pnt = new GMapMarkerPlus(mid);
                                 pnt.Tag = new midline() {now = now, next = next};
@@ -7357,6 +7364,7 @@ private void MainMap_MouseDown(object sender, MouseEventArgs e)
                 return;
 
             MouseDownStart = MainMap.FromLocalToLatLng(e.X, e.Y);
+            MouseDownStartLocal = e.Location;
 
             //   Console.WriteLine("MainMap MD");
 
@@ -7526,16 +7534,34 @@ private void MainMap_MouseMove(object sender, MouseEventArgs e)
                 }
                 else // left click pan
                 {
-                    double latdif = MouseDownStart.Lat - point.Lat;
-                    double lngdif = MouseDownStart.Lng - point.Lng;
-
                     try
                     {
                         lock (thisLock)
                         {
                             if (!isMouseClickOffMenu)
-                                MainMap.Position = new PointLatLng(center.Position.Lat + latdif,
-                                    center.Position.Lng + lngdif);
+                            {
+                                // incremental delta avoids direction lock when crossing pole singularities
+                                int dx = e.X - MouseDownStartLocal.X;
+                                int dy = e.Y - MouseDownStartLocal.Y;
+
+                                if (dx == 0 && dy == 0)
+                                    return;
+
+                                double absLat = Math.Abs(MainMap.Position.Lat);
+
+                                PointLatLng newCenter = MainMap.FromLocalToLatLng(
+                                    MainMap.Width / 2 - dx,
+                                    MainMap.Height / 2 - dy);
+
+                                if (!double.IsNaN(newCenter.Lat) && !double.IsNaN(newCenter.Lng) &&
+                                    !double.IsInfinity(newCenter.Lat) && !double.IsInfinity(newCenter.Lng))
+                                {
+                                    MainMap.Position = newCenter;
+                                }
+
+                                // key part: consume this step so next move is relative to current state
+                                MouseDownStartLocal = e.Location;
+                            }
                         }
                     }
                     catch (Exception ex)